Vulcanization systems commonly employed for epoxy group-containing elastomers in which epoxy groups function as crosslinking sites include polyamines, diamine carbamates, ammonium organic carboxylates, dithiocarbamates, and imidazoles. However, epoxy group-containing elastomers having been vulcanized with these vulcanization systems exhibit poor compression set, and achievement of satisfactory compression set requires long-time secondary vulcanization.
In order to eliminate the above-described disadvantage, various studies have been conducted on a vulcanization system which endows an epoxy group-containing elastomer with excellent compression set. For example, it has been proposed to add an organic compound having a specific structure and a quaternary ammonium or phosphonium salt to an epoxy group-containing elastomer as disclosed in JP-A-61-26620 and JP-A-63-57629 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Demand for improved compression set has recently become more and more strict. For example, excellent compression set in a high temperature atmosphere, e.g., at 180.degree. C. or even higher, has been demanded. In this connection, none of the so far proposed vulcanization systems including the above-mentioned ones does not impart excellent compression set to an epoxy group-containing elastomer even under such a severe condition.